1. Field of the Invention
This invention relates to a surface wave plasma (SWP) source and, more particularly, to a stable and/or uniform SWP source.
2. Description of Related Art
Typically, during semiconductor processing, a (dry) plasma etch process is utilized to remove or etch material along fine lines or within vias or contacts patterned on a semiconductor substrate. The plasma etch process generally involves positioning a semiconductor substrate with an overlying patterned, protective layer, for example a photoresist layer, into a processing chamber.
Once the substrate is positioned within the chamber, an ionizable, dissociative gas mixture is introduced within the chamber at a pre-specified flow rate, while a vacuum pump is throttled to achieve an ambient process pressure. Thereafter, a plasma is formed when a portion of the gas species present are ionized following a collision with an energetic electron. Moreover, the heated electrons serve to dissociate some species of the mixture gas species and create reactant specie(s) suitable for the exposed surface etch chemistry. Once the plasma is formed, any exposed surfaces of the substrate are etched by the plasma. The process is adjusted to achieve optimal conditions, including an appropriate concentration of desirable reactant and ion populations to etch various features (e.g., trenches, vias, contacts, etc.) in the exposed regions of substrate. Such substrate materials where etching is required include silicon dioxide (SiO2), poly-silicon and silicon nitride, for example.
Conventionally, various techniques have been implemented for exciting a gas into plasma for the treatment of a substrate during semiconductor device fabrication, as described above. In particular, (“parallel plate”) capacitively coupled plasma (CCP) processing systems, or inductively coupled plasma (ICP) processing systems have been utilized commonly for plasma excitation. Among other types of plasma sources, there are microwave plasma sources (including those utilizing electron-cyclotron resonance (ECR)), surface wave plasma (SWP) sources, and helicon plasma sources.
It is becoming common wisdom that SWP sources offer improved plasma processing performance, particularly for etching processes, over CCP systems, ICP systems and resonantly heated systems. SWP sources produce a high degree of ionization at a relatively lower Boltzmann electron temperature (Te). In addition, SWP sources generally produce plasma richer in electronically excited molecular species with reduced molecular dissociation. However, the practical implementation of SWP sources still suffers from several deficiencies including, for example, plasma stability and uniformity.